COLOSSUS OF RHODES is a bit of a silly film, with ocassionaly surprising violent episodes. This was pretty much an Italian trait at that time though. Even an utterly daft Maciste movie like GOLIATH AND THE VAMPIRES, which is basically a kids adventure film, features some amazing brutality (arrows through people's eys, limbs hacked off, children murdered, etc.
It true Italian style, it also has nothing to do with Goliath, and there are no vampires in it.

Back to Leone though. The best movie he was involved in before he struck gold with his Westerns was LADRI DI BICICLETTE (BICYCLE THIEVES), in which he appears as a trainee priest. He didn't get any dialogue though. He was also an assistant director on the picture.